Apparatus for vapor coating tumbling substrates



F. P. BURHAM ET AL 3,395,674

APPARATUS FOR VAPOR COATING TUMBLING SUBSTRATES Filed Sept. 23, 1963 4Sheets-Sheet 1 INVENTORS FRANCIS P. BURHAM BY ROBERT (HAMILTONATTORIVL'Y Aug. 6, 1968 F. P. BURHAM ET AL 3,395,674

APPARATUS FOR VAPOR COATING TUMBLING SUBSTRATES 4 Sheets-Sheet 2 FiledSept. 23, 1963 INVENTORS FRANCIS P. BURHAM ROBE/PT M. HA MIL TON zh dzAT T ORA/E Y Aug. 6, 1968 BURHAM ET AL 3,395,674

APPARATUS FOR VAPOR COATING TUMBLING SUBSTRATES 4 Sheets-Sheet 5 FiledSept. 23, 1963 INVENTORS FRANCIS R EUR/ AM BY ROBERT WHAM/LTO/V ATTORNEYAug. 6,' 1968 F. P. BURHAM ET AL 3,395,674

APPARATUS FOR VAPOR COATING TUMBLING SUBSTRATES 4 Sheets-Sheet 4 FiledSept. 23, 1963 F/GIS INVENTORS FRANCIS R 8URHAM ROB'RT W HAMILTON MJWATTORNEY United States Patent O 3,395,674 APPARATUS FOR VAPOR COATINGTUMBLING SUBSTRATES Francis P. Burham, Burlington, and Robert W.Hamilton,

West Burlington, Iowa, assignors to International Resistauce Company,Philadelphia, Pa.

Filed Sept. 23, 1963, Ser. No. 310,662 9 Claims. (Cl. 118-491) Thepresent invention relates to a method and apparatus for coatingarticles, and more particularly to a method and apparatus for makingelectrical resistors.

It has been previously proposed to make metal film electrical resistorsby coating a base member of an insulating material with a metal byevaporating the metal in a vacuum, and condensing the metal vapors onthe base member. For the commercial manufacturer of such resistors, itis desirable to have a coating apparatus in which a large number of basemembers can be coated at one time. Also, the apparatus should provide auniform coating on all the base members so that all the resistors ineach batch made will have substantially the same resistance value.

Heretofore, apparatus such as shown and described in US. Patent No.2,522,272 to S. A. Johnson et al., issued Sept. 12, 1950, entitledApparatus for Forming Metallic Films on Tubular Carriers and in U.S.Patent No. 2,847,- 325 to I. Risernan et 211., issued Aug. 12, 1958,entitled Apparatus and Method for Evaporating Films in Certain Types ofElectrical Components have been used for manufacturing metal filmresistors. However, such apparatus have certain disadvantages. In theapparatus of each of these patents, the base members to be coated aremounted on a wire or spindle which is mounted around the periphery of arotating drum or head. Thus, the number of the base members which can bemounted on the apparatus for a single coating operation is limited bythe length of the wires or spindles, and the diameter of the drum orhead. Also, the mounting and dismounting of the base members onto andfrom the apparatus are time consuming operations which add to theexpense of the operation.

It is therefore an object of the present invention to provide a novelmethod and apparatus for coating articles with a metal by evaporation ofthe metal in a vacuum.

It is another object of the present invention to provide a method andapparatus for coating with a metal, large quantities of cylindricalarticles at one time.

It is a further object of the present invention to provide a method andapparatus for coating with a metal, large quantities of cylindricalarticles at one time, and obtain substantially uniform coatings on allof the articles.

It is a still further object of the present invention to provide anapparatus for coating articles with a metal wherein the articles can beeasily and quickly loaded into and unloaded from the apparatus.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in thedrawings forms which are presently preferred; it being understood,however, that this invention is not limited to the precise arrangementsand instrumentalities shown.

FIGURE 1 is a perspective view of the apparatus of the presentinvention.

FIGURE 2 is a side plan view, partially broken away, of the apparatus ofthe present invention.

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2.

FIGURE 4 is a sectional View of a modification of the drum of theapparatus of the present invention.

FIGURE 5 is a sectional view taken along line 55 of FIGURE 4.

FIGURE 6 is a view taken along line 6-6 of FIG- URE 2.

FIGURE 7 is a side plan view of a modification of the evaporator of theapparatus of the present invention.

FIGURE 8 is a perspective view of the evaporator of FIGURE 7.

Referring initially to FIGURE 1, the apparatus of the present inventionin general includes a hollow, cylindrical drum 10 supported for rotationon two pairs of wheels 12-12 and 14-44. An evaporator 16 extendslongitudinally through the drum 10, and is supported substantially alongthe axis of rotation of the drum. The evaporator is connected to asource of electric current. The drum 10 is provided on its inner surfacewith a plurality of longitudinally extending projections which willcause the articles to be coated to tumble within the drum when the drumis rotated.

In use, the cylindrical bodies to be coated are poured into the drum 10,and the drum is enclosed in a bell jar 18-. The bell jar 18 is evacuatedto a pressure suitable for thermal evaporation. The drum 10 is thenrotated, and the evaporator 16 heated to the evaporation temperature ofthe metal contained on the evaporator. The metal vapors flow from theevaporator 16, and upon contacting the colder base members will condensethereon to form a film of the metal. The projections on the innersurface of the drum 10' cause the base members to tumble about withinthe drum so that the entire surface of the base members are coated withthe metal. When a film of the desired thickness is formed on thecylindrical members, the current to the evaporator 16 is turned off. Thevacuum in the bell jar 18 is then broken and the cylindrical members areready for further processing, such as terminating, thereby to be madeinto completed resistors.

Now referring in detail to FIGURES 1, 2 and 3 of the drawing, the drum10 comprises an outer cylindrical wall 20, and a pair of flat, circularside walls 22a and 22b. The outer wall 20 is provided on its innersurface with a pair of recesses 24a and 24b at the ends of the outerwall. The side walls 220 and 22b fit within the recesses 24a and 24brespectively, and are seated against the inner ends of the recesses. Apair of annular track rings 26a and 26b are mounted on and around theouter wall 20 adjacent the ends of the outer wall. The track rings 26aand 26b are secured by screws 28a and 29b respectively to three spacerbars 30 which extend longitudinally across the outer surface of theouter wall 20, and are uniformly spaced around the outer wall. Spacerbars 30 are secured to the outer wall 20 by screws 32. Track rings 26aand 26b are provided with flanges 34a and 34b respectively which projectradially outwardly from the track rings at the sides thereof adjacentthe spacer bars 30. A ring gear 36 having teeth 38 on its outerperiphery is mounted on and around the outer wall 20 next to the trackring 26b. The ring gear 36 is secured to the track ring 26b by thescrews 28b.

Side walls 22a and 2212 have central openings 40a. and 40b therethroughrespectively. Three clamping rods 42a are secured to the outer surfaceof the side Wall 22a at uniformly spaced points around the side wall22a, and project radially outwardly beyond the outer periphery of theside wall 22a. Similarly, three clamping rods 42b are secured to theside wall 22b, and project radially outward- -ly beyond the outerperiphery of the side wall 22b. When the side walls 22a and 22b aremounted within the outer wall 20, the clamping rods 42a and 42b projectthrough slots 44a and 4412 respectively in the end portions of the outerwall 20. The side walls 22a and 22b are releasably secured to the outerwall 20 by clamping members 46a and 46b respectively which engage theclamping rods 42a. and 42b respectively.

As shown in FIGURE 6, each of the clamping members 46a is L-shapedhaving a shaft portion 48a extending through and rotatably supported onthe track rail 26a, and a clamping arm 50:: extending over the endportion of the outer wall 20. A nut 52a is threaded on the end of theshaft portion 48a, and a V-shaped spring washer 54a is provided on theshaft portion 4811 between the nut 52a and the track rail 26a. Each ofthe clamping members 46a is mounted on the track rail 26a adjacent tobut spaced from a separate one of the slots 44a in the end portion ofthe outer wall 20. To mount the side Wall 22a on the outer wall 20, theclamping members 46a are pivoted to a position in which the clampingarms 50a extend radially outwardly of the outer wall 20 as shown indotted lines in FIGURE 2. The side wall 22a can then be inserted withinthe outer wall 20 with the clamping rods 42a projecting through theslots 44a in the outer wall. The clamping members 46a are then pivotedto a position in which the clamping arms 50a extend across and engagethe outer surface of the clamping rods 42a as shown in full lines inFIGURE 2. When the clamping members 46a are pivoted so that the clampingarms 50a engage the clamping rods 42a, the spring washers 54a arecompressed between the nuts 52a and the track rail 26a. The resiliencyof the spring washers 54a thereby pull the clamping arms 50a tightlyagainst the clamping rods 42a, and thereby hold the side wall 22a withinthe outer wall 20. The clamping members 46b are similar in constructionto the clamping members 46a, and are rotatably mounted on the ring gear36 and track rail 26b in the same manner that the clamping members 46aare mounted on the track rail 26a. Thus, the clamping arms 50b of theclamping members 46b engage the clamping rods 42b of the side wall 22bto secure the side wall 2212 within the outer wall 20.

As shown in FIGURE 3, the inner surface of each of the side walls 22aand 22b is lined with a sheet 56 of a metal foil. The inner surface ofthe outer wall 20 is lined with a corrugated sheet 58 of a metal foil.The metal foil liners 56 and 58 are preferably of aluminum for reasonswhich will be explained later.

The drum is supported on a base plate 60 by the two pairs of wheels12-12 and 14-14 mounted in spaced parallel relation on shafts 62 and 64respectively. The shafts 62 and 64 are rotatably mounted in bearings 66and 68 respectively which are mounted on the base plate 60. The wheels12-12 and 14-14 are in registry with the track rings 26a and 26b of thedrum 10 so that the track rings rest on the wheels, and thereby supportthe drum thereon.

A gear 70 is mounted on the shaft 62, and is in registry with the ringgear 36 of the drum so that the teeth 72 of the gear 70 mesh with theteeth 38 of the ring gear. A drive gear 74 meshes with the teeth 72 ofgear 70, and is mounted on one end of a shaft 76. Shaft 76 is rotatablysupported in a bearing 78 mounted on the base plate 60. A bevelled gear80 is mounted on the other end of shaft 76 and meshes with a secondbevelled gear 82. The second bevelled gear 82 is mounted on a shaft 84which extends through the base plate 60 and is connected to a suitabledrive means, such as a motor (not shown).

The evaporator 16 is mounted between supporting posts 86a and 861; whichare mounted on the base plate 60 adjacent opposite sides of the drum 10.The supporting posts 86a and 86b are provided with U-shaped supportingbrackets 88a and 88b respectively at the top end thereof. The ends ofthe evaporator 16 rests in the supporting brackets 88a and 88b, and aresecured therein by thumb screws 90a and 90b respectively. The evaporator16 extends through the holes 40a and 40b in the side walls 22a and 22bof the drum 10, and across the interior of the drum substantiallyparallel to the outer wall of the drum. As shown in FIGURES 1, 2 and 3,evaporator 16 comprises a heating wire of a high temperature metal, suchas tungsten or molybdenum. The

heating wire is coated with the coating metal. The evapo rator 16 can beconnected across a source of electrical current by any suitable means,such as wires (not shown) connected to the ends of the evaporator andextending through the base plate 60.

A shield supporting post 92 is secured to and electrically insulatedfrom the supporting post 86b and projects upwardly therefrom. Asupporting rod 94 is secured to the upper end of the supporting post 92,and extends through the hole 40b in the side wall 22b of the drum andacross the interior of the drum substantially parallel to the evaporator16. A U-shaped metal shield 96 extends over the supporting rod 94, andis secured thereto. The shield 96 is positioned so as to partiallyencompass the evaporator 16, and so that it opens downwardly and at a 30to 45 angle with respect to the vertical.

Posts 98 are mounted on the base plate 60 adjacent the evaporatorsupporting posts 86a and 86b. A separate shaft 100 is supported on eachof the posts 98 for slidable movement longitudinally toward and awayfrom the drum 10. A knob 102 is provided on the back end of each of theshafts 100, and a roller 104 is rotatably mounted on the front end ofthe shafts. The shafts 100 are movable between a position in which therollers 104 are over the inner surface of the end portion of the outerwall 20 of drum 10, and a position in which the rollers 104 are awayfrom the drum 10. When the rollers 104 are over the outer wall 20 of thedrum 10, they act to prevent the drum from slipping or jumping off ofthe wheels 12-12 and 14-14.

As seen in FIGURE 1, a bell jar 18 or the like is placed over the drum10 and associated mechanism to form a sealed chamber containing theapparatus. A vacuum pump (not shown) is connected to the sealed chamberin any suitable manner, such as through a hole through the base plate60, to evacuate the chamber.

To use the apparatus of the present invention the drum 10, while removedfrom the wheels 12-12 and 14-14, is loaded with the cylindrical objectsto be coated. In the manufacture of electrical resistors, the objectsare usually cylindrical rods of a ceramic material. The drum 10 isloaded with the cylindrical objects either by pouring the objects intothe drum through the center hole in one of the side walls 22a and 2212,or by first removing one of the side walls and then pouring the objectsinto the drum through the open side thereof. The loaded drum 10 is thenplaced on the wheels 12-12 and 14-14, with the teeth of the ring gear 36meshing with the teeth of the gear 70. The shafts 100 are pushed forwardto place the rollers 104 over the edge of the outer wall 20 of the drum10 so as to hold the drum on the wheels 12-12 and 14-14. The evaporator16 is placed across the interior of the drum 10, and the ends of theevaporator are clamped in the brackets 88a and 88b by the thumb screws aand 90b. The shield 96 is also secured in position across the drum 10. Abell jar 18 is then placed over the drum 10 to enclose the apparatus ina sealed chamber, and the chamber is evacuated to a pressure suitablefor thermal evacuation, usually about 0.5 micron. The drive means forshaft 84 is turned on to rotate the gear 70, and thereby rotate the drum10 around the evaporator 16. The current to the evaporator 16 is turnedon to heat the evaporator to the evaporation temperature of the coatingmetal on the evaporator.

As the drum 10 rotates, for example in the direction of arrow 106 inFIGURE 2, the cylindrical objects are carried by the corrugated liner 58from the bottom of the drum upwardly in the direction of rotation. Whenthe objects have been carried for approximately 45 of travel, the weightof the objects will cause them to drop back to the bottom of the drum.Thus, the objects are tumbled about in the lower quadrant portion of thedrum which is in the direction of rotation of the drum. When the coatingmetal on the evaporator 16 evaporates, the vapors diffuse in alldirections from the evaporator. Some of the vapors flow directly towardthe objects tumbling about in the drum 10, and the remaining vapors aredeflected by the shield 96 to flow toward the objects. As the vaporscontact the cylindrical objects they condense on the objects to form afilm. When a film of the desired thickness is coated on the objects, thecurrent to the evaporator is turned off. The rotation of the drum isstopped, and air is admitted to the bell jar 18. The bell jar 18 isremoved, and the coated cylindrical objects are unloaded from the drum10.

Since the cylindrical objects are tumbled about against the walls of thedrum 10 as the coating is being applied thereto, it is necessary thatthe liners 56 and 58, particularly the liner 58 for the outer wall 20'of the drum, be of a material which does not appreciably abrade thecoating being applied to the objects, and does not abrade onto thecoating being applied to the objects so as to contaminate the coating.It has been found that liners of aluminum foil do not appreciably abradethe coating being applied to the objects, and do not abrade away tocontaminate the coating.

Referring to FIGURES 4 and 5, there is shown a modification of the linerfor the outer wall 20 of the drum '10. The modified liner comprises aplurality of cylindrical rods 108 of a ceramic material. The rods 108are arranged in abutting, parallel relation around the interior surfaceof the outer wall 20, but spaced slightly therefrom. The rods 108 are ofa length to extend entirely across the outer wall 20 between the sidewalls 22a and 22b. A separate mounting wire 110 extends through each rod108. The ends of the wire 110 extend through the side walls 22a and 22b,and are bent to extend across the outer surfaces of the side walls so asto secure the wires to the drum 10. The rods 108 provide a corrugated,slightly resilient surface which will tumble the objects being coatedupon rotation of the drum 10. During the coating operation, the rods 108are coated with the same material as is applied to the objects beingcoated. It has been found that the coated rods 108 neither appreciablyIabrade the coating being applied to the objects, nor contaminate thecoating on the objects. Although each of the rods 108 is shown as beinga single piece, the rod can be made up of a plurality of shorter piecesmounted on the wire 110.

Referring to FIGURES 7 and 8, there is shown a modification of theevaporator which can be used in the app aratus of the present inventionfor evaporating a material which is in powdered or granulated form.Evaporator 112 comprises a sheet of a material having a high meltingtemperature, such as tungsten or molybdenum. The metal sheet is bent toform a C-shaped container portion 114, and an arcuate deflector portion116 projecting from one end of the container portion. A mounting wire118 of the same metal as the evaporator 112 is secured to one end of theevaporator to permit the evaporator to be mounted between the evaporatorsupporting posts. As shown in FIGURE 7, the evaporator 112 is positionedwith the deflector portion 116 facing toward the quadrant of the drum 10in which the cylindrical objects 120 are tumbled about during rotationof the drum. In the use of the evaporator 112, the coating material isplaced in the container portion 114 of the evaporator. An electriccurrent is passed through the evaporator 112 to heat it to theevaporation temperature of the coating material. The vapors of thecoating material diffuse from the container portion 114 and impinge onthe deflector portion 116. Since the deflector portion 116 is alsoheated, the vapors are deflected toward the cylindrical objects 120' tocoat the objects.

Thus, there is provided by the apparatus of the present invention anapparatus whereby a large number of cylindrical objects can be coated atone time since the objects are merely tumbled about in random fashionwithin the drum. It has been found that even though the objects beingcoated are tumbled about in random fashion, the coating achieved on theobjects are relatively uniform in thickness from object to object in abatch. Thus, in making electrical resistors, each batch of the coatedobjects provides a relatively tight range of resistance values. It hasbeen also found that the tumbling action dislodge loose particles of thecoating material which might otherwise cause discontinuities in the filmand adversely affect the electrical characteristics of the resistorformed therefrom. In addition, the apparatus of the present inventioncan be easily and quickly loaded and unloaded so as to reduce the timefor each coating cycle, and thereby reduce the cost of the resultantproduct.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential attributes thereof and,accordingly, reference should be made to the appended claims, ratherthan to the foregoing specification as indicating the scope of theinvention.

We claim:

1. Apparatus for coating objects by thermal evaporation in a vacuumcomprising a base plate; a pair of shafts rotatably supported on thebase plate in spaced parallel relation; a pair of wheels mounted on eachshaft with the Wheels on one shaft being in alignment with the wheels onthe other shaft; a cylindrical drum having a cylindrical outer wall, apair of flat side walls secured in the ends of said outer wall, each ofsaid side walls having a central opening therein, means secured to saiddrum and mounted around the inner surface of said outer wall providing aplurality of projections for continuously tumbling the objects beingcoated as the drum rotates, and a pair of annular tnack ringssurrounding and secured to said outer wall, the drum being rotatablysupported on said wheels with each track ring resting on a pair ofaligned wheels; a pair of evaporator supporting posts mounted on saidbase plate one adjacent each side of the drum; an evaporator containingthe coating material, said evaporator extending through the openings inthe side Walls of the drum and across the interior of the drum with theends of the evaporator supported on the supporting posts; means forheating the evaporator to evaporate the coating material; and means forrotating the drum.

2. Apparatus for coating objects by thermal evaporation in a vacuumcomprising a cylindrical drum having a cylindrical outer wall and a pairof flat circular side walls secured to and extending across the ends ofthe outer wall, each of said side Walls having a central openingtherein, means for rotating said drum about its longitudinal axis, meanssecured to said drum and mounted around the inner surface of said outerwall providing a plurality of projections for continuously tumbling theobjects being coated as the drum rotates, an evaporator containing thecoating material, means mounting said evaporator across the interior ofsaid drum, and means for heating said evaporator.

3. Apparatus in accordance with claim 2 in which the side walls of thedrum are removably secured within the ends of the outer Wall of thedrum.

4. Apparatus in accordance with claim 2 in which the means within thedrum for tumbling the objects being coated comprises a corrugated linercovering the inner surface of the outer wall of the drum.

5. Apparatus in accordance with claim 4 in which the corrugated liner isof a ceramic material.

6. Apparatus .in accordance with claim 4 in which the corrugated lineris a sheet of aluminum.

7. Apparatus in accordance with claim 6 including a separate sheet ofaluminum covering the inner surface of each side wall of the drum.

8. Apparatus in accordance with claim 4 in which the corrugated linercomprises a plurality of ceramic rods secured to the drum and arrangedin parallel contacting relation around the inner surface of the outerwall of the drum.

5 References Cited UNITED STATES PATENTS 9/1956 Mottet 118418 3/ 1964Loewen 2593X 8/1929 Buttles 117100 10 4/1948 Morgan et a1 11849 8Johnson et a1. 11849 Baer et a1. 118-49 Riseman et a1. 117-107 X Samuelet al. 117107 Wellard 117107 X Germany.

ALFRED L. LEAVITT, Primary Examiner.

A. G. GOLIAN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent'No.3,395,674 August 6, 1968 Francis P. Burham et al.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as shmm below:

In the heading'to the printed specification; lines 5 and 6,International Resistance Company, Philadelphia, Pa. should read---TRW-'In'c?'.; a corporation of Ohio Signed and sealed this 3rd day ofMarch 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, J r. Attesting Officer Commissioner of Patents

1. APPARATUS FOR COATING OBJECTS BY THERMAL EVAPORATION IN A VACUUMCOMPRISING A BASE PLATE; A PAIR OF SHAFTS ROTATABLY SUPPORTED ON THEBASE PLATE IN SPACED PARALLEL RELATION; A PAIR OF WHEELS MOUNTED ON EACHSHAFT WITH THE WHEELS ON ONE SHAFT BEING IN ALIGNMENT WITH THE WHEELS ONTHE OTHER SHAFT; A CYLINDRICAL DRUM HAVING A CYLINDRICAL OUTER WALL, APAIR OF FLAT SIDE WALLS SECURED IN THE ENDS OF SAID OUTER WALL, EACH OFSAID SIDE WALLS HAVING A CENTRAL OPENING THEREIN, MEANS SECURED TO SAIDDRUM AND MOUNTED AROUND THE INNER SURFACE OF SAID OUTER WALL PROVIDING APLURALITY OF PROJECTIONS FOR CONTINUOUSLY TUMBLING THE OBJECTS BEINGCOATED AS THE DRUM ROTATES, AND A PAIR OF ANNULAR TRACK RINGSSURROUNDING AND SECURED TO SAID OUTER WALL, THE DRUM BEING ROTATABLYSUPPORTED ON SAID WHEELS WITH EACH TRACK RING RESTING ON A PAIR OFALIGNED WHEELS; A PAIR OF EVAPORATOR SUPPORTING POSTS MOUNTED ON SAIDBASE PLATE ONE ADJACENT EACH SIDE OF THE DRUM; AN EVAPORATOR CONTAININGTHE COATING MATERIAL, SAID EVAPORATOR EXTENDING THROUGH THE OPENINGS INTHE SIDE WALLS OF THE